1. Field of the Invention
The present invention relates to an information processing apparatus and a power supply control method used in the information processing apparatus. More specifically, the invention relates to an information processing apparatus capable of mounting a plurality of processors and a power supply control method used in the information processing apparatus.
2. Description of the Related Art
In most computer systems, recently, it has been common to use a DC/DC converter on a motherboard incorporating a processor (CPU) in order to supply power to the processor. The processor increases in power consumption year by year as its operation speed becomes high. In order to react to the increase in power consumption, a DC/DC converter capable of outputting a large current is required. The power conversion efficiency of the DC/DC converter therefore has a great influence on the power consumption of the entire system.
A DC/DC converter including a plurality of power supply units is usually employed as one capable of outputting a large current. The power supply units are synchronized with each other and their total output power is supplied to a processor.
In a conventional DC/DC converter, the number of power supply units to be incorporated in the DC/DC converter depends upon the largest amount of load to be driven by the output power of the DC/DC converter. Moreover, the DC/DC converter is so designed that all the power supply units are operated at all times. If, therefore, the actual amount of load to be driven by the output power of the DC/DC converter is smaller than the largest amount of load, the power conversion efficiency of the DC/DC converter is lowered by a useless switching operation of a switching transistor in each of the power supply units.
Particularly in a computer system that is compatible to a multiprocessor capable of mounting a plurality of processors, the amount of load to be driven by the output power of a DC/DC converter greatly varies with the number of processors actually incorporated in the computer system. If, therefore, the number of processors actually incorporated in the computer system is smaller than the largest number of processors that can be incorporated therein, a number of useless power losses occur in the DC/DC converter and accordingly the DC/DC converter decreases in power conversion efficiency.